The present invention relates generally to a semiconductor device and, more particularly, to a data strobe signal generator and a semiconductor memory device including the same.
Generally, the data input circuit of a semiconductor memory device receives input data in synchronization with a data strobe signal received from an external device. Furthermore, the data output circuit of the semiconductor memory device outputs output data to the external device in synchronization with a data strobe signal. At the time of data input operation, the semiconductor memory device receives the data strobe signal from the external device but, at the time of data output operation, the semiconductor memory device generates the data strobe signal for the output of data. Therefore, the semiconductor memory device includes a strobe signal generator for generating a data strobe signal. Generally, a time point at which a data strobe signal is generated is determined by predetermined Column Address Strobe (CAS) Latency (CL). In detail, after a time (that is, the number of predetermined clock cycles) determined by the CAS Latency has lapsed from a point at which a read command is input to the semiconductor memory device, the data strobe signal generator generates a data strobe signal. Therefore, the data output circuit of the semiconductor memory device outputs output data to the external device after a time determined by the CAS Latency. In this case, it is preferable to generate (that is, toggle) the data strobe signal a predetermined time in advance of a time at which a semiconductor memory device outputs data. The reason for this is that the pulse width of the data strobe signal is not uniform during an initial interval during which the strobe signal starts to toggle. If the pulse width of the data strobe signal is not uniform, the data output circuit cannot normally output data. Therefore, the data strobe signal generates the data strobe signal during a time (that is, preamble time) that the data strobe signal takes to be stabilized. Meanwhile, as the operation speed of the semiconductor memory device increases, the operation frequency of the semiconductor memory device increases. Since the interval of internal clock signals is shortened in a high-speed semiconductor memory device, it is importance to ensure that a data strobe signal takes is stabilized. However, a conventional strobe signal generator generates a data strobe signal based on a fixed preamble time, so that it may be difficult to ensure a stabilization time during generation of the data strobe signal.